In the fabrication of integrated circuit devices, an electronic substrate, such as a wafer must be processed in numerous processing steps, i.e., as many as several hundred processing steps. During each of the processing steps, a silicon wafer must be transported in and out of a specific process machine such as an etcher, a physical vapor deposition chamber, a chemical vapor deposition chamber, etc. Between the processing steps, a preprocessed wafer is stored in a storage container called a wafer cassette. The wafer cassette is then stored in a container known as a pod to prevent contamination.
The wafer cassette is a device that is normally molded of a plastic material which can be used to store a large number of wafers in a horizontal position. In order to maximize the number of wafers that can be stored in a cassette, the wafers are positioned relatively close to each other. For instance, a pitch distance between the wafers is approximately 2 mm in a normal cassette. The wafers, when stored in the cassette are supported on their edges by molded-in supports on the interior walls of the cassette.
To load or unload a wafer into or out of a process machine or a wafer cassette, a device known as a wafer transporting blade, or a wafer blade is normally used. A wafer blade is a piece of thin metal plate that is normally formed in a rectangular shape. For instance, for loading and unloading an 8 inch wafer having a diameter of 200 mm, a wafer blade that is 150 mm long and 70 mm wide is normally used. The wafer blade is equipped with a handle portion for connecting to a robotic arm. A typical processing equipment that utilizes a wafer blade for loading or unloading wafers is one such as that manufactured by the Applied Materials Corp. of Santa Clara, Calif. In a P5000.RTM. main frame etcher, load lock chambers equipped with wafer blades are used to transport wafers into and out of various etch chambers. The chambers are used for etching of polysilicon, oxide or metal layers.
A wafer blade, when first installed, is in a perfectly flat and level condition and there is no warpage or bend in the blade. However, after repeated usage, the blade may become warped or otherwise deformed which may cause serious processing problems. When a blade, which is normally about 0.5 mm thick, is used to pick up a wafer from a wafer cassette that has only a 2 mm clearance from its neighboring wafers, a warpage or bend in the wafer blade may cause severe damage to the wafers, i.e., scratching in the surface or even breakage of the wafers. Since a wafer blade is controlled by a robotic arm which is programmed assuming that the blade is perfectly flat and leveled, even a small deviation from flatness or levelness may cause severe damage to the wafers. A reliable method for measuring the flatness or the leveling of a wafer transporting blade is therefore an important step in a preventive maintenance procedure conducted in a process machine.
Conventionally, a linear variable displacement transducer (LVDT) type of measuring device or a straight ruler are used for measuring the flatness or a deviation from a horizontal plane of the wafer blade. These types of measurement methods are not only inaccurate but also inconvenient to use when the wafer blade is normally positioned in a limited space. Moreover, a LVDT type measuring device is only capable of measuring the relative positioning of the blade, and not an absolute reading which is more desirable. A LVDT type measuring device or a straight ruler must be moved from point to point on a wafer blade and therefore there is no common reference point which can be used for obtaining an absolute reading. As a result, only a line may be established between the points and not a two-dimensional plane which is more desirable in indicating the flatness of a wafer blade.
It is therefore an object of the present invention to provide an apparatus and a method for measuring the leveling of a blade that does not have the drawbacks or shortcomings of the conventional apparatus or method.
It is another object of the present invention to provide an apparatus for measuring the leveling of a blade that is capable of providing a two-dimensional measurement in a plane.
It is a further object of the present invention to provide an apparatus for measuring the leveling and tilting of a blade that is capable of making a two-directional calibration in both a longitudinal and a lateral direction, simultaneously.
It is another further object of the present invention to provide an apparatus for calibrating the leveling and tilting of a wafer transporting blade that can be used to measure the blade in both a length direction and a width direction, simultaneously.
It is still another object of the present invention to provide an apparatus for calibrating the leveling of a wafer transporting blade which can be advantageously used in a limited space in which the blade operates.
It is yet another object of the present invention to provide an apparatus for calibrating the leveling of a wafer transporting blade wherein a two-dimensional calibration of a plane of the blade can be made.
It is still another further object of the present invention to provide a method for calibrating the leveling of a wafer transporting blade by first measuring the deviation on measuring scales provided on a calibration block and then correcting any deviations from the measuring scales.
It is yet another further object of the present invention to provide an apparatus for calibrating the leveling of a wafer transporting blade wherein the apparatus is equipped with a body portion and a leg portion which are spaced apart at a distance slightly larger than a width of the wafer transporting blade.